Android：对主活动使用后退按钮会导致错误强制关闭

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)
{
    if (keyCode == KeyEvent.KEYCODE_BACK)
    {
       //do smth
    }
    return super.onKeyDown(keyCode, event);
}

import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class Customer extends ListActivity
{
    TextView selection;
    CustomerListItem[] items = { 
            new CustomerListItem(\"Start Trip\", StartTripActivity.class), 
            new CustomerListItem(\"Clock in\", ClockinActivity.class), 
            new CustomerListItem(\"Customer Svc\", CustomerSvcActivity.class), 
            new CustomerListItem(\"Independent Inspection\", InspectionActivity.class), 
            new CustomerListItem(\"Pick Up\", PickUpActivity.class), 
            new CustomerListItem(\"Log Out\", LogoutActivity.class)};
    private TextView resultsTxt;

    @Override
    public void onCreate(Bundle icicle)
    {
        super.onCreate(icicle);
        setContentView(R.layout.main);
        setListAdapter(new ArrayAdapter<CustomerListItem>(
                this, android.R.layout.simple_list_item_1, items));
        selection = (TextView) findViewById(R.id.selection);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id)
    {
        super.onListItemClick(l, v, position, id);
        final Intent intent = new Intent(this, items[position].getActivity());
        startActivityForResult(intent, position);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent)
    {
        super.onActivityResult(requestCode, resultCode, intent);
        if (resultCode == RESULT_OK)
        {
            // Perform different actions based on from which activity is
            // the application returning:
            switch (requestCode)
            {
                case 0:
                    // TODO: handle the return of the StartTripActivity
                    break;
                case 1:
                    // TODO: handle the return of the ClockinActivity
                    break;
                case 2:
                    // TODO: handle the return of the CustomerSvcActivity
                case 3:
                    // TODO: handle the return of the InspectionActivity
                    break;
                case 4:
                    // TODO: handle the return of the PickUpActivity
                    break;
                case 5:
                    // TODO: handle the return of the LogoutActivity
                    break;
                default:
                    break;
            }
        }
        else if (resultCode == RESULT_CANCELED)
        {
            resultsTxt.setText(\"Canceled\");
        }
    }
}

import java.util.Date;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;



public class ClockinActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.clockin);
        Thread myThread = null;



        Runnable runnable = new CountDownRunner();
       myThread= new Thread(runnable);   
        myThread.start();

   }

   public void doWork() {

   runOnUiThread(new Runnable() {
       public void run() {
           try{
       TextView txtCurrentTime= (TextView)findViewById(R.id.lbltime);
                   Date dt = new Date();
                   int hours = dt.getHours();
                   int minutes = dt.getMinutes();
                   int seconds = dt.getSeconds();
                   String curTime = hours + \":\"+ minutes + \":\"+ seconds;
                   txtCurrentTime.setText(curTime);
       }catch (Exception e) {

       }
       }
   });

   }

   class CountDownRunner implements Runnable{
       // @Override
       public void run() {
               while(!Thread.currentThread().isInterrupted()){
                   try {
                   doWork();
                       Thread.sleep(1000);
                   } catch (InterruptedException e) {
                           Thread.currentThread().interrupt();
                   }catch(Exception e){
                   }
               }



Button btn = (Button) findViewById(R.id.btn_OK);

//---event handler for the OK button---
btn.setOnClickListener(new View.OnClickListener() 
{
    public void onClick(View view) {
        Intent data = new Intent();

        //---get the EditText view--- 
//        EditText txt_username = 
//            (EditText) findViewById(R.id.txt_username);

        //---set the data to pass back---
       // data.setData(Uri.parse(
           // txt_username.getText().toString()));                           
        setResult(RESULT_OK, data);

        //---closes the activity---
        finish(); 
    }
});  
}
}
}

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;



public class LogoutActivity extends Activity {
    private Button btnLogout;
    private Button btnCancel;
    private TextView lblResult;
    private EditText code;
    @Override
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.logout);

        code = (EditText)findViewById(R.id.codeout);
        btnLogout = (Button) findViewById(R.id.submit);
        btnCancel = (Button) findViewById(R.id.cancel);
        lblResult = (TextView)findViewById(R.id.result);

        btnLogout.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String logout = code.getText().toString();

                if (logout.equals(\"99999\")){
                    lblResult.setText(\"Logout successful\");

                    Intent i = new Intent(getApplicationContext(), Login.class);
                    startActivity(i);
                } else {
                    lblResult.setText(\"Logout failed\");

                }
            }
        });

         btnCancel.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {

                Intent i = new Intent(getApplicationContext(), Customer.class);
                startActivity(i);

            }

    });


}}